really, dint get your problem.

if you are sending the value through the serial port, where from and why are you reading from?

you should clear RI before returning from the interrupt and issue a RETI so that you can get the next byte. RETI is exit from the interrupt, so that you can return to it for the next one. yuou cannot read two bytes within a single interrupt.

as for sbuf retaining the old value, i dint really consider it, since the first thing we do is read the sbuf to a variable or a register. we check the variable or the register for subsequent need for that serial byte.

if you need to process the byte right within the ISR, you may do it, but you cannot look ahead for the next byte.

girish